One major issue that consistently arises in Gemini 3 that did not happen in Gemini 2.5 (this is mostly an issue in Pro, I do not notice it as much in Flash) is that it consistently inserts placeholders even when explicitly prompted that it is working with production code. It will state “in a real implementation we would”/etc and insert massively simplified codeblocks.
Claude Sonnet does not have this issue. One solution I propose to fix this is to potentially add to the main instruction/system prompt for the model to try to discern whether the user’s code is for production or just for software architecting/conceptual system design, in which case black box placeholders would be acceptable, but injecting placeholders by default is slightly dangerous for those who might be new to software engineering (even though they should be unit testing) or are taking a hands-off approach to development. I think at least a warning should be provided by default that placeholder code was used.